With the development of science and technology, the demand for materials difficult to process and novel advanced materials is increasing day by day, and higher requirements are proposed for the processing efficiency, the processing quality and the processing precision of key parts and components. The traditional grinding methods are inevitable to generate greater grinding forces and grinding heat, resulting in a series of problems such as damages to surfaces/subsurfaces of workpieces, low service lives of grinding wheels and the like. Especially in the field of precision and ultra-precision processing, and the existence of these processing defects seriously hinders the improvement of the processing precision and the processing efficiency of the parts and components.
Therefore, it is very necessary to reduce the grinding force and the grinding heat and improve the grinding quality and efficiency in a grinding process.
Nanofluid micro-lubrication grinding not only inherits all the advantages of micro-lubrication grinding, but also solves the heat exchange problem of the micro-lubrication grinding processing, thereby being a green and environmentally-friendly grinding processing technology with high efficiency and low power efficiency. Based on the heat transfer enhancement theory that the heat exchange capability of solid is greater than that of liquid and the heat exchange capability of liquid is greater than that of gas, a certain amount of nanoscale solid particles are added to degradable trace lubricating oil to generate nanofluid, and the nanofluid is atomized by high pressure air and is conveyed into a grinding area in a jet flow manner. The high-pressure air mainly plays the functions of cooling, removing abrasive dust and conveying the fluid; the trace lubricating oil mainly plays a lubricating function; the nano particles improve the heat exchange capability of the fluid in the grinding area so as to achieve a cooling function, and meanwhile the nano particles have good wear resistance and friction reduction properties and high carrying capacity, so that the lubricating effect of the grinding area is further improved, the surface quality and the burn phenomenon of the workpieces are significantly improved, the service life of the grinding wheel is prolonged, and the working environment is improved.
Ultrasonic vibration refers to converting 220V or 380V AC into ultrasonic frequency electric oscillation signals with power of 300 W and frequency of 16 kHz via an ultrasonic generator and applying the electric signals to a transducer to produce mechanical vibration with the same frequency, the amplitude of the vibration is amplified by an amplitude modulator, and a large enough mechanical vibration amplitude is finally produced on the end part of a tool. The ultrasonic generator is mainly composed of an oscillator, a voltage amplifier, a power amplifier, an output transformer and other components. The oscillator is the core of the ultrasonic generator. According to the needs of ultrasonic processing, the output waveform of the ultrasonic generator can be a sine wave or a non-sine wave, but the sine wave is the most common. An ultrasonic transducer is an energy conversion device that converts an alternating electrical signal into a sound signal or converting a sound signal in an external sound field into an electrical signal within an ultrasonic frequency range, and the commonly used transducers include hysteresis transducers and piezoelectric transducers. An ultrasonic amplitude modulator is an important component of an ultrasonic system, it is used for transferring mechanical energy converted from the electric energy transmitted by the transducer to a processed workpiece, and the ultrasonic amplitude modulator is a mechanical amplification stage of power ultrasonic amplitude and is used for improving the ultrasonic processing effect. In the grinding processing, in a plastic deformation process of the workpiece material, the deformation amount of the processed surface and the abrasion degree of grinding wheel are all related to the interaction conditions of contact surfaces between abrasive particles and the workpiece in the grinding process, that is to say, are related to their time and space conditions. When the ultrasonic vibration is applied to the process system, the interaction conditions of various contact surfaces between the abrasive particles and the workpiece are greatly different from those of ordinary grinding. Although small-amplitude high-frequency vibration generates no influence on the size and shape of the surface of the workpiece, but greatly changes the friction and wear conditions of the abrasive particles to produce additional reciprocating motion on the contact surfaces between the abrasive particles and the workpiece, so that the contact surfaces between the abrasive particles and the workpiece generate cyclical separation, grinding liquid can better enter a friction area between the grinding wheel and a workpiece interface to reduce the generation of the grinding force and the grinding heat, and the outflow resistance of the abrasive dust can also be reduced so as to efficiently clean the abrasive dust in the grinding area. Moreover, the ultrasonic vibration causes the abrasive particles to produce intermittent cutting action, while the impact load makes the material of the workpiece be convoluted more easily, more micro cracks are generated in a cutting area to reduce the grinding force and the friction coefficient. The plastic deformation of the material in the grinding process occurs mainly in sliding friction and plowing action phases, as the ultrasonic vibration grinding is pulsed intermittent grinding, the proportion of the sliding friction and plowing is relatively reduced, so that the grinding energy is reduced, and the surface thermal damage is also significantly reduced.
In the prior art, the implementation of an ultrasonic vibration grinding tool includes a connecting piece matched with a shank of a numerical control machine tool or a drilling machine, the connecting piece is used for connecting an ultrasonic vibration grinding compound processing tool with the shank of the numerical control machine tool or the drilling machine, different connecting pieces can be made according to different shanks, and this structure can be detached at any time to achieve multiple purposes of one machine. A main spindle is installed on the connecting piece, a transducer is installed on the main spindle, the transducer is connected with an amplitude change rod, a cutter is installed on the amplitude change rod, and the transducer is connected with an ultrasonic generator through a carbon brush. The ultrasonic vibration is applied to the main spindle, which involves the reformation of the machine tool, thereby being difficult to achieve, moreover, it is hard to guarantee the precision of the ultrasonic vibration applied to the main spindle of the machine tool, and the dissipation to the main spindle is relatively large, so that further improvement and optimization are needed.
A low-temperature cooling and nano particle jet flow micro-lubrication coupled grinding medium supply system includes at least one micro-lubrication and low-temperature cooling nozzle combination unit which is arranged on a side face of a grinding wheel cover of a grinding wheel and is matched with the workpiece on a worktable; the unit includes a micro-lubrication atomizing micro-nozzle and a low-temperature cooling nozzle, the micro-lubrication atomizing micro-nozzle is connected with a nanofluid pipeline and a compressed air pipeline, and the low-temperature cooling nozzle is connected with a low-temperature cooling liquid pipeline; the nanofluid pipeline, the compressed air pipeline and the low-temperature cooling liquid pipeline of each unit are connected with a nanofluid supply system, a low-temperature medium supply system and a compressed air supply system through control valves, and the nanofluid supply system, the low-temperature medium supply system and the compressed air supply system are connected with a control device. In the present invention, the low-temperature cooling is combined with nano particle jet flow micro-lubrication, thereby reducing the grinding heat and achieving a good cooling effect, but no double optimization effect is achieved on the aspect of grinding force.
An ultrasonic vibration assisted grinding device includes a disc-shaped turntable lower base, a disc-shaped turntable upper base, an amplitude change rod clamping device lower base, an amplitude change rod clamping device upper base, an ultrasonic generator connected with an amplitude change rod and a workpiece supporting platform arranged on a dynamometer, the disc-shaped turntable lower base and the disc-shaped turntable upper base are in concentric locating rotary connection, and the amplitude change rod is fixed between the amplitude change rod clamping device lower base and the amplitude change rod clamping device upper base in a convolution clamping manner. The ultrasonic vibration on any direction is achieved by the precise rotation of the turntable lower base and the turntable upper base; the workpiece supporting platform plane can be conveniently adjusted to be horizontal in the convolution clamping manner; and the dynamometer is only connected with the turntable lower base, and thus the forces on three directions of the grinding wheel can also be measured when the amplitude change rod rotates at any angle. In the present invention, an ultrasonic vibrator is supported by a supporter with a disc and has only one supporting point, so that the stability of the system cannot be guaranteed. Moreover, the one-dimensional ultrasonic vibration grinding has its limitations and needs to meet certain processing parameter conditions to achieve an ideal processing effect.
In summary, in the prior art, the relative movement trajectories of the abrasive particles of the grinding wheel and the workpiece are consistent, excessive damage to a cutting edge is caused easily by the long-term operation, the grinding wheel needs to be re-polished, thereby delaying the processing period of the workpiece; and moreover, the workpiece is unlikely to be cooled due to the long-term operation, thereby generating thermal damage to the workpiece easily. In addition, the grinding force and the grinding temperature cannot be detected in real time and online in the prior art.